RELAY PROTECTOR FOR ENERGY SYSTEMS THAT HAVE A LOGICAL CIRCUIT OF DISTANCE MEASUREMENT FILTER BY
OMISSION
TECHNICAL FIELD This invention relates generally to protective relays of power systems, and more particularly, it refers to a distance type protective relay that determines whether or not there is an existing fault within a particular protection zone for the relay, for example, within a distance of zone one from the relay.
BACKGROUND OF THE INVENTION The distance relays determine, typically by analysis _ and _ c_mpampation-r- = of ~ impecclancia, 'if there is one, particular failure in the' line of energy within a particular zone (scope) of protection for the relay. , for example, a zone one reach. The distance relay calculates an impedance value and then compares that value against a pre-set adjustment value, also referred to as the set range value, for the zone one distance. If the calculated value is less than the range value established for zone one, it is recognized that the fault is within zone one. Then a signal is produced that disconnects through the circuit breaker for that portion of the power line. If the calculated value is greater than the established range value, which indicates that the fault is outside zone one, there is no disconnection signal, produced. Distance type protective relays are designed and arranged to cover several "zones" along a given portion of a power line. The distance for a particular area is referred to as the "reach" of the area. In this way, a protective relay will usually have. several protection zones and will have adjustment values associated with each zone. Each zone is associated with a particular distance along the energy line associated with the relay. To make sure that the fault is within a selected zone of protection, for example, the zone j-ino, SjS _._ determines ^: a ~ ^ "canticulate analogous to ... the real-distance" "to the fault, using For example, replication impedance values, polarization voltage, as well as current and voltage samples of the power line.This analogous quantity, referred to in the "present as N quantity or value, provides a reliable indication of both the direction of the fault, that is, if it is in front of or behind the relay, and an indication of a sub-impedance condition in the selected zone, when the quantity m is compared against a preselected adjustment value. This is explained in more detail in U.S. Patent No. 5,325,061, owned by the assignee of the present invention, the contents of which are incorporated herein by reference. Faults in the power line that produce a m value less than the set range value associated with zone one result in a trip signal for the associated circuit breaker. However, faults in the power line that produce a m value greater than the set range value are beyond the range of the selected protection zone, indicating that the relay must not disconnect the circuit breaker associated with this zone of protection. protection. Typically, this arrangement produces fast and accurate results in relation to faults within the selected protection zone. However, when a value is broken, which is only slightly greater than the established range value, an inaccurate decision of disconnection can be made. and variations in the current voltage values of the power line may result in the value m varying over time.In some cases, the m value will vary such that at certain time points, it will go above the established range value. , and a disconnection signal is generated, although the fault may be outside the protection zone, therefore, there is an interest of accuracy with respect to the existing systems where the value m is very close to the range value established for a selected zone of protection, meaning that the fault is close to the limit of the protection zone.It would be desirable for a protection system to have the capacity to make consistent, accurate determinations of failure in relation to the protection zone. to a selected area of protection despite how close the fault is at the end of the zone.
Brief Description of the Invention Accordingly, the present invention is a system for improving the performance of a distance type protective relay for power systems, wherein the relay includes a calculation circuit sensitive to voltage and current values of the Line. of "energy" to produce a quantity (quantity -m-in-the-present) that is analogous to the distance between the relay and a fault in the power line, where the quantity is applied to a distance element for comparison of the quantity with an adjustment range value to a selected protection zone, wherein the system comprises: a filter circuit sensitive to the quantity to filter the quantity before the quantity is applied to the element away, which results in smoothing or adjusting the quantity; and a control circuit for controlling the application of the filtered amount to the distance element such that the filtered amount is applied only when the amount is above a preselected first threshold value.
Brief Description of the Figures Figure 1 is a block diagram of the system of the present invention. Figure 2A is a diagram showing a portion of the system of Figure 1. Figure 2B is a diagram showing another portion of the system of Figure 1. Figure 3 is a plot of the calculation path of m as it approaches to the established range value.
The present invention relates to a distance protective relay for power lines, which determines a quantity, referred to herein as a value m, which is analogous / is related to the distance of the relay to a fault in the power line and then it compares that m value to an adjustment value of zone one, also referred to herein as an established range value, to determine whether the fault is within or not of the particular protection zone, eg, zone one of protection , associated with the adjustment value. If the fault is within protection zone one, then the relay will disconnect the circuit breaker associated with the power line, while it is determined that the fault is outside the zone one distance, then the relay will not operate , that is, it will not disconnect the circuit breaker. Occasionally, as discussed above, the m value will be quite close to the adjustment value associated with zone one of protection, that is, the fault is quite close to the end (the far range) of the zone. With the measurement of noise and some variations in the current voltage, the m value will vary in time and the inaccurate results may result, that is, the m value may indicate that the distance ^ -a-la ^ fa-r a is ~ * inside "zone one of protection (or vice versa), when in fact the opposite is true.An inaccurate decision of distance is of course undesirable.Figure 1 shows the block diagram of the present invention. In the conventional manner, the voltage values and the current values of the power line are used to calculate the quantity M. Again, the quantity m (value) can be calculated in various ways, including as discussed herein? 061. The m value is used to determine whether the distance of the fault from the relay is within, or not, the desired protection zone of the relay, for example, zone 1. In Figure 1, the voltage values 12 they are used with the current values 14 of the power line in the system 10 by the calculation circuit 16 to determine the m value. The m value of the circuit 16 is then applied to a filter 18. The filter 18 is used to soften the m values of the circuit 16 by attenuating the noise that is present in the signal, as well as to smooth the variations in the current voltage inputs. . The m filtered, resulting value is referred to as ms for smoothed m. The original value of circuit 16 is not softened. The resulting most value, as well as the value m of the circuit 16, it is applied to a conventional distance element 20, through a switch 19. The quantity = a ~ the-output 'of the switch 19, is m' The distance element -20 can be an electromechanical element or can be implemented in a microprocessor relay (digital) The output of circuit 20 of the distance element is used to control the associated circuit breaker (not shown) in the manner described above, in particular, when the value m 'is greater than the range value set, the relay does not produce a disconnect signal to its associated switch, whereas when the signal m 'is smaller than the set range value, the distance element will produce a disconnect signal that operates the switch. The advantage of the circuit of Figure 1 with respect to existing circuits is that by smoothing the original m-value by using a filter, the accuracy of the output improves, particularly when the m-value is very high. close to the established range value, that is, the accuracy of the determination of whether the fault is within zone one is improved. The filter 18, however, is not always connected in the system 10, that is, it is sometimes bypassed. In the selected moments, it connects in the system, and in other moments it is not. This is achieved by the selection logic circuit 21, which operates in a
applies directly from the distance element 20, in a conventional manner. The logic circuit 21 determines when the filter 18 is going to be in the circuit, that is, when the ms values become values m 'and are sent to the distance element 20. The filter 18 is derived when the value m of the circuit 16 is above, up to now of the range value established for the selected area that virtually ensures that the result is indeed within the selected protection zone. In this case, the filter 18 is not needed for accuracy. While it is perhaps advantageous from an accuracy point of view that the filter 18 is almost always in the system 10, and does not increase the time required to reach a decision of disconnection / non-disconnection from the distance element 20, i.e. the filter 18 takes some time to produce a signal over an incoming m signal. This results in a longer time before a disconnection decision is made by the distance element 20; In certain cases, a failure will last longer in this way than would otherwise be the case. The threshold value of m to change the switch 19 can be varied significantly. There is a value that has the threshold
adjustment, the unfiltered m value will be applied to the distance element, which results in a faster determination of the failure, whereas when the m value is 0.5 of the adjustment value or above, the filtered m value will be applied to the element distance, which increases the time to make a determination, due to the action of the filter, but improves the accuracy. A typical filter delay interval is about 1-2 cycles of the power system, but it will depend on the actual implementation of the filter.
In a more typical situation, the threshold m to change the switch 19 to pass the ms values is adjusted in the anticipated error of the total system. For example, if the error in the system was determined to be 8%, then the threshold value will be selected to be 92% (0.92) of the set range value. The threshold can also be set slightly down for safety, for example, the error ratio plus 5%, so that the threshold is 87%, producing a safety factor beyond the actual error rate. This can also be varied. The filter circuit 16 in the mode shown is an infinite impulse response filter, although this particular type of filter is not critical. The filter must be able to reject fluid and smooth the calculation of m due to
msk is = 0.6 ¾mx + 0.4 'ms (k-1) The above equation is based on successive samples of voltage and currents. The most immediate calculation of ms, referred to in the equation as mSk, is based on the value of (the kth input not smoothed to the filter) and p? the last softened, previous filter output. This is an example of a filter calculation. Certainly other calculations can be used. A part of the selection logic circuit for the switch 19 is shown in Figure 2A. In this mode, the threshold percent value (the variable k) is set to 0.92 of the established range value. However, it must be understood again that this threshold (the value of de k) can be varied significantly. The threshold value (k-established range) is applied to an input 22 of a comparator 24. In the other input 28 to the comparator 24 is the calculated m value of the circuit 16. The output of the comparator 24 in line 29 (the output "S") is applied to the switch 19, which controls the input to the distance element 20, which is selected between the non-smoothed m value and the smoothest value of the filter 18. In Figure 2A, when the S output of the comparator is one (high), the input m 'to the distance element 20 is equal to the value m of the circuit 16, while when j3 is "zero - (- low) - and" m "- - - - - - - to ms of the filter 18 .. ..... The arrangement of Figure 2A, in the logic circuit 21 of selection in Figure 1, makes the smoothed / unmoored decision for the input to the distance element. The use of ms according to the accuracy of the distance relay, while the use of m retains the original speed of circuit 10. It is recognized that the improved accuracy results in a decrease in speed. In Figure 2B a modification of the system 10 is shown, which is also part of the selection logic circuit 21 and the filter speed is increased, that is, the delay caused by the filter decreases. Figure 3 makes some comparisons between the path of the m value during a fault for several circuit conditions. Curve 23 (unfiltered) in the center approximates the established range value (line 31) but varies or is disturbed to a degree due to noise and variations in voltage and current inputs. The m value "settles" rather quickly, instead. The ms (filtered) value is curve 24, which is smoother than curve 23 but takes a bit more to settle to its final value. Line 35 shows the established range value of 0.92 analyzed above. The delay caused by the filter is particularly a condition ... cpn-re-l-aci'on - ^ a "failure that produces a_ value, m that is significantly less than the established range value (line 31), as it is illustrated by curve 33. The fault represented by curve 33 can damage the power system (or parts of it) and should be isolated as quickly as possible is a nearby fault.) However, the filter delays the action Figure 2B shows a portion of the logical section 21 that increases the velocity through the filter.When the power system is faultless, the calculated m, produced by the circuit of Figure 1 will be substantially greater than the range value set "for zone 1. In fact, it is typically more significant than four times (400%) the set range value.This large m-value signal will operate to change the output of smoothing filter 18 to a large number When you pr If a fault is present, then it takes a longer time for the filter output (ms) to decrease to a number close to the threshold value. While the actual real value m of the circuit 16 can decline rapidly, the filter 18 can not respond as quickly. This is responsible for the delay of the operation introduced by the filter. In the present invention, when the value m of the circuit 16 begins to decrease from its high value without failure due to a failure ^ reach-another: ~ umb "ra (second) selected in relation to the established range value of the area (determined by the variable c in Figure 2B), in this case four times the established range value of zone one (line 42 in Figure 3), filter 18 is immediately loaded to only four times (400%) of the value of Therefore, instead of the output of the filter 18 you have to define for a specific time from a value that is still typically four times significantly above the set range value, as you try to follow the decrease in the value m its output, the filter output changes immediately (decreases) to the selected threshold value (but still significantly above the first threshold value) thus saving some response time of the filter. of c, as long as it is shown to be 4 by the illustration, may vary, depending on speed and safety considerations. With reference to Figure 2B, when the value m on line 34, which will be significantly higher, typically that four times the range value established for a line without failure, decreases the threshold value on line 36, due to the failure condition in the power line, the output on line 40 (signal P) of comparator 38 changes from zero to one (low to high). This signal then applies to__f_i_ltr _18; = rrque-a ^ su-veT-T ^ preload or change the filter -a four times the range value set, in the particular mode shown (example) .This filter change -to a value less than which would otherwise be at that point in time from the start of the fault and the beginning of the decrease of the value m saves time in the total decrease of the output of the filter 18 as follows the input m. Figure 2B pre-loads the filter, however, it will not completely eliminate the delay caused by the filter, rather it will decrease the delay and therefore improve the total speed performance of the relay. times (400%) the set threshold value, depending on the individual system and the relay For example, it may be that the relay calculates a value m that is not much greater than four times the range value set during a condition without failure, under these circuits In this case, the threshold value on line 36 to comparator 38 and the pre-change value applied to filter 18 can be significantly less than four times the set range value. While the circuit of Figure 2B is advantageous, it does not have to be included with the circuit of Figure 2A.
understand that several changes, modifications and substitutions of the invention can be incorporated without departing from the spirit of the invention, which is defined by the following claims: